最小生成树(无向图)
Kruskal
给所有边按从小到大排序 形成环则不选择(利用并查集)
P1546 最短网络 https://www.luogu.com.cn/problem/P1546
#include<iostream> #include<cstdio> #include<string> #include<algorithm> typedef long long ll; using namespace std; struct Node { int x, y, w; friend bool operator < (const Node& a, const Node& b) { return a.w < b.w; } }; Node a[200002]; int pre[200002]; int Find(int x) { return pre[x] == x ? x : pre[x] = Find(pre[x]); } int main() { int n, k, cnt = 0; scanf("%d", &n); for (int i = 0; i < n; i++) { pre[i] = i; for(int j=0;j<n;j++){ scanf("%d", &k); if (j > i) { //矩阵只需判断一半 a[cnt].x = i; a[cnt].y = j; a[cnt++].w = k; } } } sort(a, a + cnt); int ans = 0; int p = 0; for (int i = 0; i <cnt; i++) { if (Find(a[i].x) != Find(a[i].y)) { ans += a[i].w; pre[Find(a[i].x)] = a[i].y; p++; if (p == n - 1) break; } } printf("%d\n", ans); return 0; }
HDU 1875 http://acm.hdu.edu.cn/showproblem.php?pid=1875
#include<iostream> #include<cstdio> #include<string> #include<algorithm> typedef long long ll; using namespace std; struct Node { int x, y; double w; friend bool operator < (const Node& a, const Node& b) { return a.w < b.w; } }; Node a[6000]; //数组注意开大 int pre[105]; double x[105]; double y[105]; int Find(int x) { return pre[x] == x ? x : pre[x] = Find(pre[x]); } double dis(double x1, double y1, double x2, double y2) { return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2)); } int main() { int T,c; scanf("%d", &T); while (T--) { int cnt = 0; scanf("%d", &c); for (int i = 0; i < c; i++) { pre[i] = i; scanf("%lf%lf", &x[i], &y[i]); for (int j = 0; j < i; j++) { double dist = dis(x[i], y[i], x[j], y[j]); if(dist>=10.0&&dist<=1000.0){ a[cnt].x = i; a[cnt].y = j; //printf("%d %d\n", a[cnt].x, a[cnt].y); a[cnt++].w = dist;} } } sort(a, a + cnt); double ans = 0; int p = 0; for (int i = 0; i < cnt; i++) { if (Find(a[i].x) != Find(a[i].y)) { ans += a[i].w ; pre[Find(a[i].x)] = a[i].y; p++; if (p == c - 1) break; } } if (p == c - 1) printf("%.1f\n", ans*100); else printf("oh!\n"); } return 0; }